Method of aging titanium base alloys



METHOD OF AGlNG TIT BASE ALLOYS .SchnylerA. l-llerres, Las Vegas, andThomas K. Redden,

Boulder City, Nev., assignors to Allegheny Ludlum Steel Corporation,Breckenridge, Pa., a corporation of Pennsylvania No Drawing. Originalapplication September 29, 1949,

Serial No. 118,723. Divided and this application 3am!- 'ary15, 1954,Serial No. 404,392

' 3 Claims. (Cl. 148-4130) This invention relates to new and improvedprocedure for making titanium base alloys, and to alloys producedthereby.

Since titanium is a relatively new metal, the production of its alloyshas heretofore been more or less on a laboratory scale. Since it isrecognized that titanium has a great afiinity for contaminatingmaterials in the production of its alloys, it has heretofore been thepractice to employ relatively pure alloying elements. This has made theproduction of such alloys almost prohibitive in cost and has limitedtheir field of application.

Pure titanium metal which, itself, is not commercially obtainable, isvery soft and ductile. It has been indicated that annealed high puritytitanium metal has a tensile strength of about 32,000 p. s. i., a yieldstrength of about 17,500 p. s. i., 55% elongation, and 73 Brinellhardness. Commercially available titanium sponge metal melted intoingots without appreciable contamination, forged into bars, and annealedat 1500 F. on an average, has a tensile strength of about 70,000 p. s.i., a yield strength of about 60,0000 p. s. i., 30% elongation, andabout 160 Brinell hardness. The higher strength and hardness and thelower ductility is accounted for by the impurities, particularly oxygen.

Although a relatively high ductility of metal is required forfabricating cold drawn tubing, and this indicates the use of titaniummetal of the highest practical purity, we have determined that for mostapplications, titanium alloys with strength and hardness much betterthan those obtained for commercially pure metal are needed. Since theweight of titanium is only about 60% of that of steel, titanium alloyswith tensile strengths exceeding 140,000 p. s. i. and having moderateductility, i. e., about will compare favorably with best alloy steelsand aluminum-base alloys for structural uses, such as aircraft enginesand frames, turbines, etc. The superior strength per unit weight oftitanium alloys together with their excellent corrosion resistance willmake it possible to reduce the dead weight of moving parts intransportation and power generating equipment with a resultantsubstantial increase in operating efficiency.

Additions of nitrogen, oxygen, carbon, iron, tungsten, molybdenum, orchromium as binary alloys with tita- 2,819,194 Patented Jan.,7, 1958nium gave the following results:formhot-forgedand annealed alloys:

We have determinedthat combinations of oxygen or nitrogen with. theelements chromium, molybednum,:and tungsten or iron, manganese andnickel'provide more beneficial results than the use of any of the singleele ments. Pure chromium, molybdenum, tungsten or manganese arerelatively scarce and expensive. 1 Thus, if, as has been the, practiceheretofore, relatively pure metals are employed, the expense becomesprohibitive.

In endeavoring to find a solution to the problem'thus presented, wediscovered that ferroalloys of these metals which are easily preparedand readily available, are the most economical means of adding alloyingmetals to titanium. They not only are suitable for making titaniumbasealloys of the desired ternary and higher order, but alsoproduceevenbetteralloys than those produced 'by the introduction of pure elements.We have determined that the harder metals, such as chromium, molybdenum,tungsten or manganese. become more readily soluble in molten titaniumwhen they are introduced as ferroalloys, and that thepresence of ironcomplements and enhances the effects of the chromium, molybdenum, etc.This is believed to be an outsanding development in the art although itis directly contrary to: prior teaching as to the making oftitanium-base alloys. 11: not only provides an improved product,-.but amuch more economical one.

In accordance with our procedure, oxygen or nitrogen additions may bemade as titanium dioxide or titanium nitride compounds which are alsocommercially available or may be incorporatedwith the ferroalloy. A highnitrogen grade of ferrochromium is commercially obtainable in severalanalysis ranges, for example, suchas chromium, 33%, iron, and 1.4%nitrogen. The following table is representative of properties obtainedin forgediiand annealed titaniumihathas been cooled with properadditions of ferrochromium, ferromolybdenum, ferrotungsten, andferromanganese, with or without supplementary additions of nitrogen oroxygen:

4 content of the chromium or iron or both of them, a high temperaturebody-centered cubic lattice structure of titanium is stabilized andretained at room temperature. This Table II Hard- Tensile Yield Elong,Alloy Addition, Percent ness. Strength, Strength, Percent BH p. s. i p.s. i

1 .04 N, 2.0 Cr, 275 120,000 107, 500 22 2 .25 N, 2.0 Cr, 330 153, 500133, 000 18 3- .25 N, 2.0 Cr. 340 162, 000 148, 000 4- .05 N, 3.4 CI,330 156, 000 142. 000 16 5- .25 N, 3.4 Ct. 360 172,000 151,000 6. .05 N,4.2 Cr, 330 154. 000 140. 000 17 7.-- .1 N, 4.1 Cr, 1. 340 160, 000 145.000 15 8 .2 N, 4.2 Oz, 1. 380 183, 000 174, 000 13 9 .1 N, 5.0 Cr, 2.388 189, 000 3 10.-.- .2 N, 8.0 Cr, 3. 345 168,000 153, 000 0 11 .2 N,10.0 C1, F 350 176, 000 163, 000 13 12 .05 N. 14.0 Cr, 9 Fe 360 15 13.25 N, 3.0 M0, 405 7 14---- .25 N, 2.5 W, 315 15 .25 0, 3.5 0r, 340 1916 .25 O, 2.5 W, 310 140, 500 H 20 17-- .25 N, 5.0 Fe 420 207, 000186,000 3 18 .25 N, 5.0 Mn 370 173, 000 160, 000 16 The alloys of TableII may be summarized as follows:

The following table gives percentage analysis ranges for titanium-basealloys of improved characteristics that have been produced in accordancewith our procedure: Table III 0= 02-.40 0=.02-.40 A Fe 75-10 A:Fe=4.0-7.0

Or=l.5-l4.0 Gr=8.014.0 N=.05.25 N=.05.20 B Fe=.75-7.0 B: Fe=4.07.0

Cr=1.514.0 1 Cr=8.014.0 N=.02-.25 o=.02-.40 C 0=.02-.40 C N=.02-.25 Cr=15-200 2 =4.0-7.0 Fe= 75-100 =s.014.o

o=0.02-0.40 =0.0t r0.40 D Fe=0.53.0 E Fe- .5 =0.02-0.30

Mo=1.0-5.0 Mo=l.0-5.0 =0.5-3.0 =1.0-5.0 0=0.02-0.40 N=0.020.40=0.02-0.40 G Fe=0.52.0 H Fe=0.52.0 =0.02-0.40

w=1.5-5.0 W=l.5-5.0 =0.5-2.0 =1.55.0 0=0.02-0.40 N=0.02-0.25 =0.02-0.40.I Fo=0.1-3.0 K Fe= 1-3.0 =0.02-0.a0 Mn=1.07.0 Mn-I 0-7 0 =0.1-5.0

65 i? N=.1- o=.1-.3 {Mn=2.0-6 o {Mn=2.0-6.0 .02-.20

LgllO N=.1.25 0= -3 .0 .0 i Fe=2.5-6.0 l re 02-.20

The alloys of Table III may be used in various conditions of heattreatment depending upon the specific properties desired. Hot workingwithin a temperature range of about 1400" to 1800 F., followed bycooling in air produces desirable properties for most structural uses. Asubsequent anneal or stress relief is, however, preferred to obtainuniformity of properties. This is accomplished by reheating to atemperature within the range of about 1200 to 1606 F. and cooling at asuitable rate. Alloys A B C and E to M, inclusive, respond favorably toheat treatment and may be hardened by rapid cooling, as water quenchingfrom temperatures above about 1500 F., or softened by relatively slowcooling from the same temperature.

Alloys A B C and D respond favorably to heat treatment of a differenttype from the above groups. On heating to a temperature above about 1500F. and cooling at a rate that may be slower, the higher the provides asofter, more ductile metal than is obtained if the same alloy is cooledsufiiciently slowly to alloy the titanium and transform it to its normalhexagonal close packed lattice structure.

All of the alloys of Table III may be hardened somewhat followingmoderately rapid cooling from a temperature above about 1200 F., by anaging or precipitation hardening mechanism on reheating and holding forvarious periods in the temperature range of about 700 to 1200 F. Thetime of holding is less, the higher the aging temperature in this rangeand the effect is reversible, so that the alloy may be softened again byreheating to a higher temperature. All the alloys may also be hardenedby cold working, i. e. mechanical reduction in crosssectional area attemperatures below about 1200 F. and may be softened again by heating totemperatures above about 1200 F. for various periods, the temperatureand time employed in the softening operation will depend on the degreeof cold work accomplished.

All of the alloys and commercially pure titanium may be surface hardenedby heating in air or atmospheres, mixtures, or fused baths that providenitrogen or oxygen for combination with the titanium. It has been found,for example, that titanium heated in the presence of oxygen for aboutone hour at 1900 F. is hardened for a depth of .050 of an inch below thesurface with a maximum surface hardness of 400 Brinell. Similar surfacehardening effects are produced by heating titanium or the alloys innitrogen-rich atmospheres, such as ammonia gas at temperatures as low as950 F. The depth and degree of hardness produced is controlled by thetime and temperature of exposure as Well as the composition of theatmosphere or bath used.

In accordance with our preferred procedure, all elements are made fromcommercially available titanium metal, such as produced by the reactionof chemically pure titanium tetrachloride with magnesium metal and whichcontains approximately .02% nitrogen, .1% oxygen, and .l% iron as theprincipal impurities. We prefer to produce our titanium alloys inaccordance with the Herres arc-melting procedure (see application filedSeptember 13, 1949, Serial No. 115,454, now abandoned) which is carriedout in a Water-cooled copper crucible and in an atmosphere that isnon-contaminating of the titanium. Also, the alloys may be prepared byany melting or powder metallurgy technique that will produce metal ofthe desired chemical composition. In accordance with our procedure,ferromctal, and particularly, ferrocompounds of one or more of theelements chromium, molybdenum, tungsten, or manganese are added to thetitanium While it is in a molten state and while an ambient atmosphereis maintained that is non-contaminating of the titanium. Such additionsmay be eifected through an air lock into an enclosed furnace or crucibleWhile a titanium halide is being reduced therein.

In accordance with such procedure, the titanium halide or compound uponreduction is immediately converted to molten metal to which the alloyingadditions may be made. A proportionate amount of nitrogen and oxygen ora combination of them may be made to obtain the desired ultimate contentof the alloy as indicated by the tables.

Our heat treatment as set forth herein, although specifically worked outfrom the standpoint of titanium-base alloys of a ternary or high order,and particularly, ternary or higher alloys containing iron, may be usedwhere applicable to other titanium alloys as indicated herein.

In Table III A, B, and C represent broader ranges of the alloys withintheir representative groups, while alloys A A B B and C and C arepreferred ranges within the specified broader ranges.

Alloys M, M, N, and 0 when made by the additions of ferromanganese, maycontain a small amount of iron and oxygen as impurities, for example,about .1% or less, each, relatively small percentages of such impuritiesdo not appear to have deleterious elfects in these managanese alloys,although they can be substantially removed by well known procedure.

It should be noted that the specific alloys 17, 18 (P' and M) of column3 and M to R, inclusive, of column 3 are, in themselves, the soleinvention of Thomas K. Redden, and that their disclosure herein is made(Without prejudice to his rights therein) to show that iron or ferroadditions are beneficial, and to better or more completely illustratethe procedure for making and conditioning titanium-base alloys whichwith the other alloys (except those above specifically listed)constitute our joint invention or inventions.

As to alloys A B C and D, it has been found that with normal impuritiesof about .02% nitrogen, about .1% oxygen, and .1% iron, a chromiumaddition will retain the body-centered structure on water quenching, butnot on air cooling, while a chromium addition will retain it on aircooling. An alloy of 4.8% iron and 10% chromium with .2% nitrogen, and.1% oxygen as impurities, will retain the body-centered cubic structureon air cooling. It thus appears that the combination of iron andchromium definitely favors retention of such structure. Small amounts ofoxygen or nitrogen appear beneficial in improving the properties of thebodycentered structure alloys, but in general, appear to have anon-controlling influence as to the body-centered lattice structure. Inany event, a body-centered lattice structure is assured bywater-quenching alloys containing about 4% iron and 8% chromium throughthe upper limit of about 7% iron and 14% chromium.

This application is a division of application Ser. No. 118,723, filedSeptember 29, 1949, now abandoned.

What we claim is:

1. A method of conditioning a ternary and higher titanium base alloywhich is responsive to the following defined treatment and whichconsists essentially of an alloying gas selected from the groupconsisting of nitrogen and oxygen with a range of .02 to .40% each, analloying metal selected from the group consisting of and within thespecified ranges of about .1 to 10% iron, 1.5 to 20% chromium, 1 to 5%molybdenum, 1.5 to 5% tungsten, and 1 to 10% manganese, and theremainder titanium which comprises, aging and precipitation hardeningthe alloy by heating and holding it within a temperature range of about700 to 1200 F.

2. A method as defined in claim 2 wherein the alloying gas is introducedinto the titanium base alloy by ferroalloy additions to a moltentitanium melt.

3. A method of conditioning as defined in claim 2 wherein the alloy ispreliminarily hardened by heating it to a temperature above about 1200"F. and is moderately rapidly cooled from such temperature before thealloy is aged and precipitation hardened.

References Cited in the file of this patent UNITED STATES PATENTS1,674,959 Dean June 26, 1928 2,169,193 Comstock Aug. 8, 1939 2,317,979Dean et a1 May 4, 1943 2,520,753 Ball et al Aug. 29, 1950 2,554,031Jafiee et al. May 22, 1951 2,588,007 Jafiee Mar. 4, 1952 OTHERREFERENCES Preparation and Evaluation of Titanium Alloys, SummaryReport; Part III covering the period May 18, 1948,

to July 30, 1949.

Patent No. 2,819,194

U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTIONJanuary '7, 1958 Schuyler A Herres et a1,

appears in the printed specification I It is hereby certified that errorcorrection and that the said Letters of the above numbered patentrequiring Patent should read as corrected below.

read 60,000 column 3,, in the Column 1, line 35,, for "60,0000" summaryof Table II, second column thereof, last line for "Fe: 050" read Fe=5.,0column 6, lines 23 and 26 for the claim reference numeral '2', eachoccurrence, read l Signed and sealed this 1st day of April 1958 (SEAL)Attest: I

KARL mAXLINE ROBERT c. WATSON C'omnissioner of Patents Attesting Officer

1. A METHOD OF CONDITIONING A TERNARY AND HIGHER TITANIUM BASE ALLOYWHICH IS RESPONSIVE TO THE FOLLOWING DEFINED TREATMENT AND WHICHCONSISTS ESSENTIALLY OF AN ALLOYING GAS SELECTED FROM THE GROUPCONSISTING OF NITROGEN AND OXYGEN WITH A RANGE OF .02 TO .04% EACH, ANDALLOYING METAL SELECTED FROM THE GROUP CONSISTING OF AND WITHIN THESPECIFIED RANGES OF ABOUT .1 TO 10% IRON, 1.5 TO 20% CHROMIUM, 1 TO 5%MOLYBENUM, 1.5 TO 5% TUNGSTEN, AND 1 TO 10% MANGANESE, AND THE REMAINDERTITANIUM WHICH COMPRISES, AGING AND PRECIPITATION HARDENING THE ALLOY BYHEATING AND HOLDING IT WITHIN A TEMPERATURE RANGE OF ABOUT 700* TO1200*F.